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    <h2>大小写转换</h2>
    原数据：<input id='old' type="text"><br>
    操作：
     <input type="button" value="转大写" onclick="deal('upper')">
     <input type="button" value="转小写" onclick="deal('lower')"><br>
     新数据：<input id="new" type="text">
     <script>
         function deal(opt){
             var str = document.getElementById('old').value;
             switch(opt){
                 case 'upper':
                 str = str.toUpperCase();
                 break;
                 case 'lower':
                 str = str.toLowerCase();
                 break;
             }
             document.getElementById('new').value = str;
         }
     </script>
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